The invention relates to an assembly of an electric machine as well as to an electric machine with such an assembly.
Definitions
The term “assembly of an electric machine” as used herein refers both to a stator and a rotor of an electric machine in the form of an internal or external rotor machine. An electric machine in this context may be an electric motor as well as an electric generator. The invention is applied, in particular, to rotary machines of all kinds (synchronous, asynchronous, reluctance, permanent field machines or the like).
State of the Art
In the state of the art it is known to build the magnetically conducting parts of a machine (in particular of an alternating current machine) of laminations because of the otherwise occurring eddy currents. For the core assemblies, typically single or double-sided insulated sheet panels of a thickness between 0.35 mm and 1.5 mm of dynamo sheet metal (hot rolled electric-quality sheet) are cut to correspondingly shaped strips. From these strips stator and rotor laminations with respective recesses are punched, whereby it is aimed at producing as little scrap as possible. The stator and rotor laminations manufactured in this manner are stacked upon each other and united under pressure to laminated cores in which the recesses of the individual laminations form grooves for the stator or rotor windings to be subsequently installed.
If the individual sheet metal layers of the rotor or stator are manufactured as integral parts (so-called round plates), the punching scrap is considerable. In order to reduce the punching scrap, only annular segments (of e.g. 30°) are therefore manufactured, packeted to 8 to 10 mm high stacks and stacked above each other laterally overlapping in an annular shape. In order to prevent the individual sheet metal layers of such a laminated core or the overlapping cores to separate from one another they can be stabilised by means of through joints, synthetic resin, rivets, or the like. Rotors which are manufactured in this manner, however, have a limited maximum speed because their strength in the radial direction is not very high. Correspondingly, the natural frequency of stators which are manufactured in this manner is relatively low which results in increased damping expenditures.
From DE 36 09 368 A1 it is known to manufacture magnetic circuits of electric machines by forming cores from punched magnetic sheet metal. The cores are formed by superposing of sheets. For connecting the individual cores, these comprise in a first embodiment connector lugs at their areas facing towards each other and correspondingly shaped connector recesses. The connector lugs and the connector recesses are designed in such a manner that they join the cores by simply sliding them into each other. The superposed magnetic sheets of the individual cores are joined by welding along a vertical line. This weld serves to hold the individual cores together in a compact arrangement. In a second embodiment, the magnetic sheets lying above each other are welded to the magnetic sheets of an adjacent core along a vertical line to form a magnetic circuit of the stator.
From DE 11 40 638 it is known to connect rotors of electric machines where several sheet metal layers of the sheet metal segments result in a layer, and several layers result in the core height of the rotor. The connection is made by bolts which are inserted through holes in the sheet metal segments. The abutment areas of the sheet metal segments are staggered from sheet metal layer to sheet metal layer by one hole distance or an integral multiple of such a distance. The document discusses strength questions in detail which arise from the use of bolts in holes of overlapping sheet metal segments.
From DE 974 711 it is known to utilise an adhesive joint in lieu of the chaining bolts required at the overlapping sites for the transfer of the tangential forces caused by centrifugal forces.
From DE 692 04 322 T2 (=EP 0500 457 B1) it is known to make a stack of layers, with each layer consisting of at least two partial circular arc-shaped sheet metal elements. These sheet metal elements are joined with each other at the abutting sides by means of three alternatingly oriented dovetails. The individual layers are stacked in such a manner that the sheet metal elements are partially overlapping.
From DE 1 961 941 B, a dynamo machine with staggered ring segments is known, where the individual segments are provided at the radially outer circumferential area with a plurality of equally spaced dovetail serrations. The field poles are arranged at these radially outer dovetail serrations. Incidentally, the ring segments of this arrangement, too, are provided with holes for through bolts which keep the structure together.
DE 100 28 097 A1 discloses a rotor for an electric motor which comprises an armature which together with the bars and rings forms a cast composite body. In the manufacture of the rotor the sheet metal laminations are combined to laminated cores, and neighbouring laminations in the laminated core are tack-ed together by spot welding. In this manner, axially extending spot welds are generated. At two diametrically opposed outer sides of the armature one bandage each is then applied. The sheet metal laminations have a circular shape.
Problem on which the Invention is Based
Starting from the initially described restrictions and drawbacks of known assemblies for electric machines, the invention is based on the problem to fundamentally change these assemblies in terms of their manufacture in order to render them significantly more economic and allow their use in electric machine with high speeds or low natural frequencies, respectively.
Inventive Solution
The inventive solution of this problem is an assembly of an electric machine with at least two abutting circular ring or circular disk-shaped sheet metal layers, each of the sheet metal layers being formed by several circular ring or circular disk-shaped sheet metal segments which are arranged concentrically about a centre axis, two of which are abutting under the formation of a connecting joint and comprising a predetermined minimum cross-sectional area in the radial direction, and with the sheet metal segments of abutting sheet metal layers partially overlapping in the circumferential direction and being joined by welds along the circumferential area, with the number of welds between a connecting joint of two sheet metal segments of a sheet metal layer and a connecting joint of two sheet metal segments of a neighbouring sheet metal layer being calculated in such a manner that the sum of the effective areas of these welds is at least approximately equal to the predetermined minimum cross-sectional area of the sheet metal segments.
This completely novel design of electric machines or their assemblies, respectively, is advantageous in that virtually the maximum speed as with assemblies (rotors) made from integral round plates or comparable natural frequencies as with assemblies (stators) made from integral round plates can be achieved, although a reduction in punching scrap and manufacturing costs of up to 25% can be realised by the invention.
Advantageous Developments of the Invention
In a preferred embodiment of the invention, the connecting joint of the circular ring or circular disk-shaped sheet metal segments is oriented essentially radially. It is, however, also possible to provide the edges of the sheet metal segments which together form the connecting joint with such a structure that the sheet metal segments can be hooked or locked together. This, too, contributes to provide stability.
The welds can be arranged both at the outer and the inner circumferential area of the sheet metal segments.
It is, however, also possible to arrange some of the welds at the outer circumferential area and some at the inner circumferential area of the sheet metal segments. This applies, in particular, to assemblies whose inner diameter is relatively small and whose outer diameter is relatively large so that the minimum cross-sectional area of the sheet metal segments is also relatively large. If the individual segments of such configurations are to be relatively small (e.g. 30°), it may be necessary to arrange welds both on the inner and outer circumference.
The welds are preferably formed essentially circular or oval and are made by laser welding.
The sheet metal segments to be joined by welds of abutting sheet metal layers overlap each other in the circumferential direction by 20 to 70%, preferably by 50%. It is, however, also possible to vary the extent of overlapping or to so select the extent of overlapping that the connecting joints are staggered from one sheet metal layer to the next along the circumference.
If the sum of the welds along the circumference of the sheet metal segments of abutting sheet metal layers were not sufficient, it is possible to additionally close the connecting joint of two adjacent sheet metal segments of a sheet metal layer by means of welds at least partially in the area of the circumferential area. This can also be carried out both at the inner and the outer circumferential area.